U.S. patent number 6,601,679 [Application Number 09/946,997] was granted by the patent office on 2003-08-05 for two-part wireless communications system for elevator hallway fixtures.
This patent grant is currently assigned to Otis Elevator Company. Invention is credited to David Crenella, Michael P. Gozzo, Richard R. Grzybowski, Jeffrey M. Izard, Robert G. Morgan, Chester J. Slabinski.
United States Patent |
6,601,679 |
Crenella , et al. |
August 5, 2003 |
Two-part wireless communications system for elevator hallway
fixtures
Abstract
Elevator system hall fixtures such as lanterns, hall call button
switches and lights, gongs, and floor position indicators are
connected to a controller via wireless transceivers. The controller
can be a system, group, and/or car controller. A low power wireless
system connects all fixtures on one hallway, with a higher power
wireless system connecting each hallway with the appropriate
controller.
Inventors: |
Crenella; David (Berlin,
CT), Gozzo; Michael P. (Groton, CT), Grzybowski; Richard
R. (Corning, NY), Izard; Jeffrey M. (Bolton, CT),
Morgan; Robert G. (Bolton, CT), Slabinski; Chester J.
(New Hartford, CT) |
Assignee: |
Otis Elevator Company
(Farmington, CT)
|
Family
ID: |
25485327 |
Appl.
No.: |
09/946,997 |
Filed: |
September 5, 2001 |
Current U.S.
Class: |
187/395; 187/247;
187/391 |
Current CPC
Class: |
B66B
1/3415 (20130101); B66B 1/3446 (20130101); B66B
1/34 (20130101) |
Current International
Class: |
B66B
1/34 (20060101); B66B 001/34 () |
Field of
Search: |
;187/371,393,395,396,397,399,247 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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27 33 441 |
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Aug 1979 |
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DE |
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1 067 714 |
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Oct 2001 |
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EP |
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403046979 |
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Feb 1991 |
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JP |
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408316720 |
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Nov 1996 |
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JP |
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11150505 |
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Feb 1999 |
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JP |
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00/34169 |
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Jun 2000 |
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WO |
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00/34170 |
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Jun 2000 |
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WO |
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Primary Examiner: Salata; Jonathan
Attorney, Agent or Firm: Wall Marjama & Bilinski LLP
Claims
What is claimed is:
1. An elevator system in a building having a plurality of
hoistways, each hoistway having an elevator cab moving therein to
provide service to a plurality of floors in said building,
comprising: a plurality of hall fixtures at each floor including at
least one service call request button switch for requesting service
along said hoistways in a corresponding direction, and a service
call request button light for each of said service call request
button switches; connection means for connecting each of said hall
fixtures on each floor to a high power electromagnetic floor
transceiver located on a same or adjacent floor in close proximity
thereto; a controller having a high power electromagnetic
controller transceiver operatively associated with each of said
floor transceivers for exchanging electromagnetic messages between
each floor and said controller; and said floor transceivers
transmitting to said controller transceiver messages indicating the
activation of one of said service call request buttons, said
controller transceiver transmitting messages to selected ones of
said floor transceivers to cause a service call request button
light to be turned on in response to registering a corresponding
service call request for that floor and to be turned off in
response to one of said elevator cabs approaching the related floor
to provide service; wherein the fixtures on each floor include, for
each of said hoistways, a set of one or more hall lanterns
including an up direction hall lantern on each floor except the
highest floor and a down direction hall lantern on each floor
except the lowest floor; wherein said controller transceiver
transmits messages addressed to the transceiver of a selected floor
to cause a corresponding one of said lanterns to light in response
to one of said elevator cabs approaching said selected floor to
provide service thereto, and transmits messages to the transceiver
of said selected floor to turn off a corresponding lantern in
response to closing of the door of a corresponding elevator cab
stopped at said selected floor; and wherein said controller
comprises a group controller portion having a transceiver
communicating with said floor transceivers, and a plurality of car
controller portions, each car controller portion having a
transceiver communicating with corresponding ones of said fixture
transceivers.
2. An elevator system according to claim 1, further comprising: at
least one gong for each floor, said controller transceiver
transmitting messages addressed to said floor transceiver of a
selected one of said floors, which messages are passed on to a
selected fixture transceiver associated with said at least one gong
for causing said gong to sound as one of said cabs approaches said
selected floor to provide service thereto.
3. An elevator system in a building having a plurality of
hoistways, each hoistway having an elevator cab moving therein to
provide service to a plurality of floors in said building,
comprising: a plurality of hall fixtures at each floor including at
least one service call request button switch for requesting service
along said hoistways in a corresponding direction, and a service
call request button light for each of said service call request
button switches; connection means for connecting each of said hall
fixtures on each floor to a high power electromagnetic floor
transceiver located on a same or adjacent floor in close proximity
thereto; a controller having a high power electromagnetic
controller transceiver operatively associated with each of said
floor transceivers for exchanging electromagnetic messages between
each floor and said controller; and said floor transceivers
transmitting to said controller transceiver messages indicating the
activation of one of said service call request buttons, said
controller transceiver transmitting messages to selected ones of
said floor transceivers to cause a service call request button
light to be turned on in response to registering a corresponding
service call request for that floor and to be turned off in
response to one of said elevator cabs approaching the related floor
to provide service; and first and second transceivers on each
elevator cab, wherein said controller transceiver operatively
associated with each of said floor transceivers for exchanging
electromagnetic messages between each floor and said controller is
operatively associated via said first and second transceivers on
each elevator cab.
4. An elevator system according to claim 3, wherein: the fixtures
on each floor include, for each of said hoistways, a set of one or
more hall lanterns including an up direction hall lantern on each
floor except the highest floor and a down direction hall lantern on
each floor except the lowest floor; and said controller transceiver
transmits messages addressed to the transceiver of a selected floor
to cause a corresponding one of said lanterns to light in response
to one of said elevator cabs approaching said selected floor to
provide service thereto, and transmits messages to the transceiver
of said selected floor to turn off a corresponding lantern in
response to closing of the door of a corresponding elevator cab
stopped at said selected floor.
5. An elevator system according to claim 4 wherein said controller
is a group controller.
6. An elevator system according to claim 5 wherein said controller
comprises a group controller portion having a transceiver
communicating with said floor transceivers, and a plurality of car
controller portions, each car controller portion having a
transceiver communicating with corresponding ones of said fixture
transceivers.
7. An elevator system according to claim 6, further comprising: at
least one gong for each floor, said controller transceiver
transmitting messages addressed to said floor transceiver of a
selected one of said floors, which messages are passed on to a
selected fixture transceiver associated with said at least one gong
for causing said gong to sound as one of said cabs approaches said
selected floor to provide service thereto.
8. An elevator system according to claim 4, further comprising at
least one gong for each floor, said controller transceiver
transmitting messages addressed to said floor transceiver of a
selected one of said floors, which messages are passed on to a
selected fixture transceiver associated with said at least one
gong, for causing said gong to sound as one of said cabs approaches
said selected floor to provide service thereto.
9. An elevator system according to claim 4, further comprising at
least one direction-indicating lantern for each of said floors,
said controller transceiver transmitting messages addressed to a
floor transceiver at one of said floors, which messages are passed
on to a selected fixture transceiver associated with said at least
one direction-indicating lantern for causing said lantern to
indicate the direction of travel of one of said cabs approaching
said selected floor to provide service thereto.
10. An elevator system according to claim 9 wherein said lantern
consists of an "up" direction indication for each floor served by
said elevator except the highest floor and a "down" direction
indication for each said floor except the lowest.
11. An elevator system according to claim 3, wherein said
connection means comprises a low power fixture transceiver
associated with each hall fixture and a low power transceiver
associated with said floor transceiver.
12. An elevator system according to claim 11, wherein said
electronic messages between said controller transceiver and said
floor transceivers are in spread spectrum format.
13. An elevator system according to claim 3, wherein said
transmissions between said controller transceiver and one of said
first and second transceivers on each elevator cab include
controller to cab communications.
Description
FIELD OF THE INVENTION
This invention relates to systems for moving people and freight,
such as elevators, in which wireless electromagnetic transmissions
are used to communicate between the fixtures at each stop (such as
hall fixtures of an elevator) and a controller, in order to respond
to and inform passengers of the stops, and in particular, to a
two-part wireless system that uses a low power system to
communicate between hall fixtures and a high power system to
communicate to and from a group or system controller.
BACKGROUND OF THE INVENTION
A conventional elevator system group has a "riser" which includes,
for each floor, at least one up hall call request button with an
associated light to indicate that the group controller has
registered the request (except for the highest floor), at least one
down hall call request button with an associated light to indicate
that the group controller has registered the request (except for
the lowest floor), and at least one gong for providing an audible
indication that a cab is about to arrive. In addition, on each
floor, each elevator hatchway has associated with it a set of
lanterns that identify which of the elevators is about to arrive,
and depending on which of the lanterns is lit, the direction in
which the elevator is currently traveling. The highest and lowest
floors have only one lantern in a set of lanterns, whereas the
remaining floors have two lanterns per set. In addition, cab
position indicators are provided for each elevator in the group on
major floors such as lobby floors, which indicate the current floor
position of the corresponding elevator cab. Herein, floor position
is taken to be equivalent to the committable floor of the cab (that
is, the next floor where the cab could possibly stop, or a floor
where it is stopped).
Regardless of how many individual processors are utilized,
multi-elevator groups employ a car controller for each car, with a
group controller for the entire group, or a distributed controller
which provides both car and group functions. Each car controller
communicates with the corresponding elevator car by means of a
traveling cable, and the various car controllers communicate with
the group controller over cables. In turn, the group controller
communicates over wires with the hall fixtures previously
described.
In large systems, such as several groups each having 15-25 floors,
the amount of wire involved in enormous. Whenever upgrading is to
be achieved, modifications to the elevator wiring (which is
embedded in the building) can be extremely difficult, if not
sufficiently prohibitive so as to confine the nature of the upgrade
to that which will conform to the wiring. When upgrades or new
elevator systems are to be provided in occupied buildings, the time
required to rewire or reconfigure the wiring of a building can be
prohibitive due to the need to have minimal intrusive shutdown of
elevators during the work, so that use of portions of the elevator
system by paying tenants can continue throughout the work
period.
Similar equipment with similar problems may be found in horizontal
transport systems as well as in systems that provide both vertical
and horizontal transportation.
Direct point to point communications have been proposed to overcome
problems associated with communicating between fixtures in elevator
hallways and the centralized controller. This potential solution
has the problem of requiring each fixture to have a relatively
powerful transmitter with concomitant complexity, leading to cost
increases and increases in power usage.
SUMMARY OF THE INVENTION
Briefly stated, elevator system hall fixtures such as lanterns,
hall call button switches and lights, gongs, and floor position
indicators are connected to a controller via wireless transceivers.
The controller can be a system, group, and/or car controller. A low
power wireless system connects all fixtures on one hallway, with a
higher power wireless system connecting each hallway with the
appropriate controller.
Elevator systems, whether horizontal, vertical, or inclined,
transmit and receive control signals via a wired network using a
time division multiple access (TDMA) protocol. The time and expense
incurred while installing the wired network can be reduced by using
wireless communication methods between floor hall call fixtures,
lanterns, and floor position indicators. The wireless fixture also
reduces the amount of time personnel have to work inside the
hoistway, an inherently dangerous environment. A low power,
unlicensed spread spectrum communication system according to the
invention has been demonstrated to perform all control functions
for an elevator hoistway system including hall calls and lantern
indications using point to point RF communications. The point to
point communication system overcomes large scale and small scale
fading effects on propagation within the elevator hoistway at
ranges up to 150 meters.
According to an embodiment of the invention, an elevator system in
a building having a plurality of hoistways, each hoistway having an
elevator cab moving therein to provide service to a plurality of
floors in the building, includes a plurality of hall fixtures at
each floor including at least one service call request button
switch for requesting service along the hoistways in a
corresponding direction, and a service call request button light
for each of the service call request button switches; connection
means for connecting each of the hall fixtures on each floor to a
high power electromagnetic floor transceiver located on the same
floor in close proximity thereto; a controller having a high power
electromagnetic controller transceiver operatively associated with
each of the floor transceivers for exchanging electromagnetic
messages between each floor and the controller; and the floor
transceivers transmitting to the controller transceiver messages
indicating the activation of one of the service call request
buttons, the controller transceiver transmitting messages to
selected ones of the floor transceivers to cause a service call
request button light to be turned on in response to registering a
corresponding service call request for that floor and to be turned
off in response to one of the elevator cabs approaching the related
floor to provide service.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified, stylized, front plan view of an elevator
system incorporating a first embodiment of the invention.
FIG. 2 is a simplified, stylized, sectioned side elevation view of
the system of FIG. 1.
FIG. 3 is a simplified, stylized, front elevation view of an
elevator system incorporating a second embodiment of the present
invention.
FIG. 4 is a simplified, stylized, front elevation view of an
elevator system incorporating a third embodiment of the present
invention.
FIG. 5 is a partially broken away, simplified perspective view of a
plurality of horizontal levels having cabs traveling thereon, the
levels being interconnected by elevator shuttles that move the cabs
vertically.
FIG. 6 is a simplified, stylized cross sectional view of an
elevator hoistway which shows an embodiment of the present
invention.
FIG. 7 is a graph showing the results of testing for elevator
hoistway path loss and 2.4 GHz ISM band maximum allowable path
loss.
FIG. 8 is a graph showing the results of testing for elevator
hoistway attenuation versus range.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, an elevator system employing the invention
serves a plurality of stops, such as floors F1-FN. In this
exemplary embodiment, there are four elevator hoistways C1-C4, each
floor F1-FN has, for each of the hoistways C1-C4, a directional
lantern set which includes a down lantern 12 for each floor except
the lowest floor and an up lantern 13 for each floor except the
highest floor. Each of the floors except the top floor FN has an up
service call request button 17 with an associated call-registered
light 18, that optionally includes the conventional "halo" or ring
surrounding the button 17. Pressing the button 17 informs the group
controller 24 that a passenger desires to travel upwardly from the
related floor; when the group controller registers the call, it
sends a signal back to light the light 18 so as to inform the
passenger that the call has been registered. Each of the floors
except the lowermost floor F1 has a down service call button 19 and
a corresponding light 20. At each stop, a gong 21 is sounded when a
car in any one of the hoistways C1-C4 is about to stop on the
corresponding floor.
Each of the hoistways C1-C4 has a corresponding car controller 23
and the group is supervised by a group controller 24. The car
controllers are interconnected with the group controller 24 by wire
cables 25. This, of course, is no difficulty since it occurs on a
machine floor where the wiring can be channeled through easily
accessible ducts, within the space, rather than in the walls. On
important floors, such as lobby floors, each of the hoistways C1-C4
has a car position indicator 26 that at any moment when the car is
in service, displays the committable position of the corresponding
car. As seen in FIG. 2, the conventional elevator cab 28
communicates with its car controller 23 by means of a traveling
cable 29.
Of course, instead of individual lights for car position indicators
26, and in place of the distinct directional lanterns 12, 13, modem
elevators may well use liquid crystal displays which include both
car position and directional information. Instead of only one gong
21 per stop, there may be one on each side of the elevator lobby,
or there may be one for each hoistway 11. A gong could be on the
car instead of in the lobby. A gong could include a portion of and
be operated with any one of the lanterns, serving one stop, or
there may be a gong associated with each set of lanterns and
operable therewith, so as to provide an audible indication of the
location of the approaching cab. The gong may be a bell; it may
generate a tone or other non-verbal sound; or it may make a verbal
announcement. Instead of a single set of service call buttons 17-20
per stop, there may be two sets for each stop, one on each side of
an elevator corridor, or more.
According to an embodiment of the invention as shown in FIG. 2, the
group controller 24 has an electromagnetic transceiver 30 which
communicates with any and all of corresponding transceivers 31 at
each stop (each floor) of the building. As used herein, the term
"electromagnetic transmission" means wireless transmission, that
is, transmission without the use of any solid media. Similarly, the
terms "transmitter", "receiver", and "transceiver", refer to
equipment which sends and receives transmissions without solid
media. In the present embodiment, it is assumed that the fixtures
have locally positioned electronics associated with them so as to
permit operation in response to commands. For instance, pressing
one of the call buttons 17, 19 causes a corresponding wireless
transmission from the transceiver 31 of the related stop indicating
a request for an up call or a down call on that floor. Similarly, a
single wireless transmission from the group controller transceiver
30 addressed to a specific one of the transceivers 31 may order it
to sound the related gong 21. These signals are thus discrete, and
are responded to in order to cause the desired action. The
remainder of the required signals are simply to either turn on or
turn off a hall button light 18, 20, a lantern 12, 13 or any of the
car position indicator lights 26. It should be understood that
whenever liquid crystal displays are used in place of discrete
lights, the required action is simply causing a commensurate change
in the template of the liquid crystal display. Alternatively,
wireless audio or video could be sent to a fixture, e.g., "GOING
DOWN."
For further understanding, consider the following sequence in which
boldface type indicates wireless electromagnetic transmissions of
the invention. This sequence of commands and responses, based on
FIG. 1, assumes there is only a floor transceiver. 1. Down button
pressed F2 2. F2 transmits "down request F2", addressed to group
controller 3. Group controller registers down call request on F2 4.
Group controller transmits "turn on down button light", addressed
to F2 5. Group controller assigns call to car 3 6. Group controller
sends "stop on F2" to car 3 controller 7. Car 3 controller sends
"committable floor car 3=F2" to group controller 8. Group
controller transmits "turn on car 3 position=floor 2" addressed to
lobby 9. Group controller transmits "sound gong, turn on down
lantern car 3, turn off down button lights", addressed to F2 10.
Car 3 stops with its door opening 11. Door of car 3 closes 12. Car
3 sends "door fully closed" to car 3 controller 13. Car 3
controller sends "door fully closed, car 3" to group controller 14.
Group controller transmits "turn off down lantern, car 3",
addressed to F2 15. Car 3 controller sends "committable floor car
3=lobby" to group controller in response to user pressing F1 on car
operating panel (COP) 16. Group controller transmits "turn on car 3
position=lobby", addressed to lobby 17. Group controller transmits
"sound gong, turn on lantern, car 3, turn off button light",
addressed to lobby
Note in the above it is assumed that the circuitry is such that
whenever a turn on request is made, a latch corresponding to the
device involved has an input such that an accompanying gating
signal turns it on if it has the input, and otherwise either turns
it off or allows it to remain off, whereby each turn on of one
light in the position indicator 26 or lantern is accompanied by
turning off of all the remaining lights. Of course, other protocols
may be used for controlling the actual fixtures.
Referring to FIG. 3, a second embodiment of the present invention
includes a plurality of electromagnetic transceivers 28 associated
with corresponding hoistways, which receive from the group
controller transceiver 30 messages to turn on and turn off the
directional lanterns 12, 13. This avoids the need to have wiring
between the floor transceivers 31 and the hall lanterns 12, 13. The
remaining functions, described with respect to FIGS. 1 and 2, are
handled in this embodiment by the floor transceivers 31. Thus, the
floor transceivers 31 will transmit service call requests and will
receive instructions to sound the gong and to turn on and turn off
the call button lights.
In the foregoing sequence, lines 9, 14 and 17 would read as
follows: 9a. Group transmits "sound gong, turn off down button
light", addressed to F2 9b. Group transmits "turn on down lantern"
addressed to car 3, F2 14a. Group transmits "turn off lanterns",
addressed to car 3, F2 17a. Group transmits "sound gong, turn off
button light", addressed to lobby 17b. Group transmits "turn on
lantern", addressed to car 3, lobby floor
Referring now to FIG. 4. instead of the group controller
transceiver 30 communicating with each of the hoistway transceivers
28, a transceiver 50 is provided on each car for each of the car
controllers 23. In this embodiment, the turn on and turn off of the
lanterns is effected by electromagnetic transmissions from the car
transceivers 50 to the transceivers 28. This embodiment allows the
group controller 31 to send only one message for each event,
because the lantern message of FIG. 3 is sent by the corresponding
car transceiver 50.
In the foregoing sequence, lines 9, 14 and 17 would be as follows:
9c. Group transmits "sound gong, turn off button lights", addressed
to F2 9d. Car 3 transmits "turn on down lantern" addressed to car
3, F2 14b. Car 3 transmits "turn off lanterns", addressed to car 3,
F2 17a. Group transmits "sound gong, turn off button light",
addressed to lobby 17c. Car 3 transmits "turn on lantern",
addressed to car 3, lobby floor
The manner in which the messages can be formulated so as to provide
an indication of the desired action and the address of the
recipient, along with error control codes and the like, may
conveniently be of the type illustrated in U.S. Pat. No. 5,854,454
incorporated herein by reference. On the other hand, protocols such
as that illustrated in U.S. Pat. No. 5,535,212, the Echelon Lon
Works communication protocol, incorporated herein by reference, or
any simplified communication protocol that will serve the purposes
herein may be utilized.
The car controllers and group controller may each be implemented in
a separate processor, may be implemented in a distributed
processing system as in U.S. Pat. No. 5,202,540 incorporated herein
by reference, or all in one processor. As used hereinafter, the
term "controller" can mean any or a combination of the foregoing.
The lanterns may be turned on and off in conjunction with other
events, when appropriate, in an elevator, for instance, turned on
at the outer door zone, turned off as the door begins to close, or
otherwise.
The embodiments described with respect to FIGS. 1-4 include
elevators, in which an elevator car includes an integral cab. The
invention may as well be used in elevators in which cabs are
carried on car frames, and can be removed therefrom for loading and
unloading, or for transport on bogeys, horizontally, and then
transported vertically once again on an elevator car frame, as
disclosed in U.S. Pat. No. 5,861,586 incorporated herein by
reference. The guideways for cabs may be elevator hoistways,
horizontal tracks or the like, or combinations of each, and the
guideways may be inclined at angles between horizontal and
vertical. Therefore, the term "hoistway" as used herein includes
hoistways, horizontal tracks, or combinations, and guideways,
whether horizontal, vertical, or inclined at angles between
horizontal and vertical.
Referring to FIG. 5, a plurality of levels 290-293 in a first
structure 294 are served by a pair of elevators 295, 296. The
structure 294 may be connected by horizontal tracks 299, 300 to a
totally different structure 301 located some distance from the
structure 294. The structure 301 may also include elevators such as
an elevator 302 into which cabs may be transferred for vertical
transportation. In FIG. 5, the elevators 295, 296 are depicted as
being employed in a scheme in which cabs will be moved upwardly to
a desired floor in elevator 295 and carried downwardly from level
291 in elevator 296. However, other schemes may be employed, that
shown being merely exemplary. As shown on the level 291, the cabs
may serve a plurality of stops 305, service to any one of which may
be requested by pressing a service call request button in the
corresponding cab or at the stop. Should a cab be loaded on the
elevator 295 with a service call for a level such as 292 or 293,
the elevator 295 can raise the cab to that level before
transferring it to a bogey on that level. Similarly, one or more
cabs may be run in a bus mode in which each cab travels around each
level and then goes to the next level and travels around it. The
mode of operation in the various horizontal levels, and therefore
the nature of exchanges between the elevators are irrelevant to the
invention, there being an unlimited number of ways in which
vertical and horizontal transportation can be combined.
In the embodiment of FIG. 5, the directional lanterns may be arrows
indicating right or left travel, or the lanterns may indicate
destinations with numbers, letters or words. Similarly, the service
call buttons may be identified with floors, as in conventional
elevator systems, or with horizontal directions, or destinations.
In a conventional elevator system, the stops are the various floors
serviced by the elevators, whereas in a horizontal transport
system, the stops may be one way stops in those cases where cabs
pass the stop only in one direction, as is implied in the levels
291-293 of FIG. 5, or they may be two-way stops where cabs can
travel past the stop in either direction.
In the embodiments of FIGS. 3 and 4, the hoistway transceivers 28
may simply be receivers if message acknowledgments do not have to
be transmitted therefrom. Similarly, the car transceivers 50 need
only be transmitters if message acknowledgments need not be
received thereat.
Referring to FIG. 6, according to one embodiment, a car such as an
elevator car 132 is shown inside a guideway such as hoistway 134. A
controller such as a group controller 130 controls the movement and
location of car 132. A link 122 communicates from a transceiver 112
and antennas 116, 118 mounted on car 132 to each fixture 124. A
second link 110 relays these signals from a second transceiver 113
in car 132 via a top-of-hoistway antenna 120 to a transceiver 114
in the machine room. This link is optionally used for car
communications between car 132 and controller 130. The
top-of-hoistway antenna 120 is preferably a high gain antenna such
as a Yagi antenna. Transceivers 112, 113 optionally share the
top-of-car antenna 116 to send and receive signals to controller
114. Transceiver 114 is connected to controller 130 via an
interface 138 which uses a network protocol such as IEEE 802.11,
TDMA, or slotted Aloha. All the links are preferably in the 2.4 GHz
unlicensed frequency band for global application, or similar band,
and use spread spectrum modulation to provide the best reliability.
Additional options include using an active repeater with processing
on elevator car 132 for intermediate stage error correction, using
a network router on car 132, interleaving/de-interleaving data for
error reduction, using an active non-processing repeater on car
132, using a bi-directional amplifier at each floor to extend the
range to adjacent hoistways, and/or using sub-networks at each
floor to extend to adjacent hoistways.
In an alternative embodiment, fixtures 126 transmit directly to the
top-of-hoistway antenna 120 via link 128. In either case,
communications to car 132 are also accommodated. Fixtures 124, 125
can be Luxury-style or other current styles with a 2.4 GHz radio
transceiver interface. Test data indicate that fixture antennas do
not need to protrude into hoistway. The need to drill holes in
walls for fixture antennas is undesirable since it requires a
second mechanic to be in the hoistway during installation to
collect the drilled-out wall material. This adds labor cost and
puts a mechanic in the hoistway, negating some of the safety
advantages of installing a wireless system.
In an alternative embodiment, the communications within each
hallway, i.e., between hall call buttons/indicators, lanterns, and
gongs, are done with a very low power system such as infrared, V,
or narrow band RF. The low power system is primarily a line of
sight (LOS) system. Each floor has a main unit that sends and
receives to the hallway fixtures on the low power system, with the
main unit also sending and receiving to the main car controller or
group controller on a higher power system that preferably uses
spread spectrum RF wireless. A bank of multiple hoistways could use
the same main unit for controller communications.
A wireless hall fixture demonstration was conducted to show that a
wireless system can meet the response time required for an elevator
system. The wireless system must also mitigate the effects of
multipath propagation and Radio Frequency (RF) interference that is
encountered in the 2.4 GHz Industrial, Scientific and Medical (ISM)
unlicensed bands. Using radio hardware that demonstrated the
selected RF channel, carrier frequency, and modulation technique,
the demo system was designed so that key parameters (response time
and bit error rate) could be easily measured and evaluated.
This demonstration had two main purposes: 1) comparing wireless
hardware operating side by side with wired hardware, demonstrating
concurrency, and 2) providing quantified test data used to
determine the engineering feasibility and validation of RF channel
and protocol software models.
Wireless fixtures were installed along side the wired fixtures on
the right side of the elevator openings at the 1st and 2nd floors
of a hoistway test tower. For the wired system, a Remote Serial
Link (RSL) interface board (RS5) is embedded in each hall call
fixture. This RS5 interface routes communication to and from the
operating controller system software and each appropriate hall call
fixture. This link is time division multiplexed (polled).
For the wireless system, a base transceiver located in the machine
room communicates directly with an RS5 interface board which gets
the information onto the existing RSL communication link. Remote
transceivers are located in the hall fixtures and interface with
the buttons and indications. This link is time division multiplexed
(polled), the same as the baseline system. In effect, the wireless
link replaced the wires running between the fixture
buttons/indicators and the RS5, with the RS5 relocated to the
machine room end of the RSL bus. In the preferred embodiment of the
invention, the communications are directly with the elevator system
controller, bypassing the RSL link.
The elevator hoistway provided a unique radiowave propagation
environment that warranted measurement and analysis. An RF signal
experiences large and small scale fading as the signal propagates
through the hoistway. Small scale fading is experienced with small
changes in position, or the position of objects in the propagation
path change, on the order of a wavelength. Large scale fading is
experienced when large changes in receiver position occur, much
greater than a wavelength. Large scale fading is commonly referred
to as path loss. The characteristics of the multipath propagation
ultimately drive the design of the communication system for optimal
performance.
The physical dimensions of a typical elevator hoistway (approx. 2.5
m.sup.2) are 20 times larger then the wavelength of a signal
transmitted at 2.4 GHz (12.5 cm). The large surfaces within the
elevator hoistway generate reflections of the original signal that
combine at the receiver to yield multipath effects. These
reflections or echoes can interfere with the primary path signal. A
measurement of the impulse response of the elevator hoistway shows
the characteristics of the multipath delay profile. This
information is used to determine bandwidth (data rate) limits and
link margin requirements. The elevator hoistway multipath is not
significantly different than other indoor multipath measurements.
The data acquired from the tests shows the RMS delay spreads and
maximum excess delays to be within the accepted ranges of values
measured in other indoor environments. Communication systems
operating in this environment with restricted RF power levels need
to employ some kind of multipath mitigation. In the present
invention, the wireless electromagnetic transmissions of the
invention are preferably spread spectrum radio frequency
transmissions to improve the reliability of the communication
system. Alternatively, spatial diversity techniques are applied for
the same purpose. Table 1 summarizes the 90-percentile confidence
point of the cumulative distribution plots for the key
characteristics of the system. Overall, the data indicate that the
degree of small scale fading encountered in the hoistway is easily
compensated for using frequency hopping spread spectrum (FHSS)
radios. Also, data rates obtainable with commercially available
FHSS LAN hardware will not be limited by small scale fading.
TABLE 1 90 Percentile Confidence Values For Key Multipath
Characteristics Coherence No. of RMS Delay Excess Delay BW Paths
Yagi to FL 2 80 ns 168 ns 16 MHz 6 Yagi to FL 11 82 ns 130 ns 16.5
MHz 5
Large scale fading versus the distance between the transmitter and
receiver and the car position within the hoistway was also
examined. Testing was also performed to measure the effect that
interference and channel loading had on the Automatic Repeat
Request (ARQ) protocol performance. Path loss experienced in free
space varies inversely proportional to the square of the distance
between the transmitter and receiver (1/R.sup.2). Free space
assumes there are no objects in or near the propagation path. Once
objects are present, the path loss experienced by a signal may be
greater than 1/R.sup.2. The amount that the exponent, the path loss
factor, increases is determined by the size and location of the
objects. In the literature, path loss factor has been shown to
range from 1.8 to 3.2 for propagation on a single floor within a
building depending on the occupancy. Propagation through floors has
been shown to increase the path loss factor in excess of five
(1/R.sup.5), depending on construction and the number of floors
passed through. Propagation though the hoistway should allow a
comparatively lower loss path over many floors as opposed to
attempting to transmit directly through the floors.
The data taken at the test hoistway were fit to these theoretical
performance curves in an attempt to determine the path loss factor
that is the best predictor for the given configuration. A program
was written to calculate the mean square error between the data for
each of the tests defined and path loss curves of varying slope,
from 0.01 to 4. This calculation was performed for each of the 364
points in the sweep over the several floors of data that was
collected. The results of the data analysis show there are several
predictors of path loss that must be used depending on the hoistway
configuration and the antenna system deployed: 1) the point to
point system yielded a path loss factor between 2 and 2.47
depending on the location of the car within the hoistway, and 2)
communication from the top of the hoistway to the car yielded a
path loss factor of 1.08.
Referring to FIG. 7, the mean path loss that can be expected for
the each of the conditions tested is shown. The maximum attenuation
that can be tolerated for a communication system with a performance
of 1.times.10-5 Bit Error Rate (BER) at -95 dBm signal strength is
shown for the maximum allowable effective radiated power (EIRP) in
the different regions of the world. These communication systems are
assumed to be using spread spectrum techniques in the 2.4 GHz ISM
band. One performance threshold is shown for a fixed carrier
system, which reduces the allowable EIRP significantly. The
performance thresholds for maximum attenuation assume no link
margin and are based on the mean received signal strength.
The large-scale fading results based on one set of data taken in
the test hoistway indicate that a path loss factor of 2 to 2.5
governs the loss through the hoistway. Furthermore, communications
at a range of 150 m should be possible with acceptable bit error
rates.
The following narrative summarizes the rationale used for system
selection. Government regulation of wireless communication systems
fall into two categories; licensed and unlicensed. Unlicensed
operation is desired due to the freedom from license applications
and spectrum coordination. Operating in the unlicensed operating
bands presents two challenges. The first is radio frequency (RF)
power limitations and the second is interference. The amount of RF
power that can radiate from the antenna, referred to as effective
radiated power (ERP), is restricted to minimize the amount of
interference an unlicensed system will cause to other communication
systems.
Interference must be avoided or handled by the unlicensed system as
best as possible because the regulations do not provide any
protection from interference in these bands. The maximum ERP and
resistance to interference is achieved by utilizing a spread
spectrum modulation method in the unlicensed bands. Regulations of
unlicensed communication systems throughout the world are not well
coordinated. The only consistent portion of the spectrum that is
available in the three regions resides in the 2.4 GHz Industrial,
Scientific and Medical (ISM) band. The ERP allowed spans from 10 mW
to a maximum of 4 W.
The measurement of the propagation characteristics, RMS delay
spread and coherence bandwidth, in the test hoistway indicate a
maximum data rate of 5 Mb/s can be supported. An elevator velocity
of 8 m/s generates a coherence time in the hoistway of
approximately 6 ms in the 2.4 GHz band. A packet length of 5 ms
will minimize channel variation within a single packet
transmission.
The propagation measurements also showed that small scale fades due
to the movement of the car experienced by a hall fixture can be as
much as 20 dB. A communication system should have at least 20 dB of
link margin, employ a signaling format to combat the fading
(frequency hopping), and/or correct errors in the data due to the
small scale fading. Small scale fading, also referred to as
frequency selective fading, creates narrow-band fades, thus
reducing the signal to noise ratio received by the radio. This
narrow-band fading has the same effect as a narrow-band jamming
signal. The effectiveness of a spread spectrum modulation against
jamming is measured by the system jamming margin. The jamming
margin of this system is 9 dB. The link margin of a spread spectrum
system can be reduced by the amount of the jamming margin to
reducing the necessary link margin.
The attenuation of a RF signal versus distance in free space varies
as the inverse of the square of the distance. The test hoistway
showed slightly worse performance than free space. Attenuation
between a transmitter and receiver can be approximated using these
results. The performance of a four node wireless communication
system operating at 250 Kb/s was able to handle a message
generation rate of 8 times what is predicted for an average
elevator. The wireless communication system utilized a collision
sensing multiple access (CSMA) protocol which is uniquely suited
for the elevator system due to the asynchronous, low message
traffic rate to and from the hall fixtures. This particular CSMA
protocol also included positive acknowledgment of received messages
and retransmission of messages with errors to improve the effective
Bit Error Rate (BER). The BER of this demonstration system was
measured to be on the order of 3.times.10-4 errors without any
retransmissions. Lower error rates were experienced with various
levels of retransmission in the same environment. The CSMA protocol
used also met the latency requirement of 100 ms one way under the
heaviest loading conditions that could be generated with four
nodes.
An example of a communication system that operates within the
bounds of the results obtained during the test and some key areas
of world wide communication regulations is presented in Table
2.
TABLE 2 Frequency Band 2.4 GHz Spread Spectrum Type Frequency
Hopping (80 MHz Bandwidth) Jamming Margin 9 dB Data Rate 250 Kb/s
Channel Bandwidth 400 KHz Noise Figure 8 dB Packet Length 5 ms ERP
10 mW (10 dBm) Receive 3 dB (fixture antenna); Antenna Gain 12-16
dB (machine room antenna) Sensitivity -95 dBm for a 1 .times. 10-5
BER (no retransmissions) Link Margin 20 dB
The rationale for each of the system selections are based on
government regulations or test results. The rationale for each
system characteristic is now described. The Frequency Band is
available in all three regions of the world and allows for spread
spectrum and maximum ERP. Frequency Hopping provides effective
resistance to multipath effects and interference and is more power
efficient than direct sequence spread spectrum (DSSS) at this time.
The Data Rate meets system performance requirements for latency and
throughput while not using excessive channel bandwidth and falls
within the bounds dictated by the hoistway propagation
measurements. The ERP is the maximum level that is usable in all
three regions of the world and is a reasonable power level for
battery power or other low capacity power supplies. The Packet
Length falls within the bounds indicated by the hoistway
propagation measurements. The Maximum Range can be improved by
changing the following parameters: a) reducing the data rate
(channel bandwidth) to improve the sensitivity, b) reducing the
receiver noise figure to improve the sensitivity, c) increasing the
ERP, d) increasing the receiver antenna gain to improve the
received signal strength, e) providing data error correction by
retransmission or coding to improve the BER at a given signal to
noise ratio, and f) employing spread spectrum techniques with
greater jamming margin to reduce the effect of multipath allowing
operation with a lower link margin.
The maximum range that can be achieved by this communication system
is plotted in FIG. 8. A point to point communication system can
achieve range of 190 m. The effect of link margin, receiver antenna
gain, ERP and jamming margin is shown on the plot. Good immunity to
unintentional jammers (microwave ovens, other 2.4 GHz freq.
hoppers) is provided by the directional pattern of the base station
antenna.
While the present invention has been described with reference to a
particular preferred embodiment and the accompanying drawings, it
will be understood by those skilled in the art that the invention
is not limited to the preferred embodiment and that various
modifications and the like could be made thereto without departing
from the scope of the invention as defined in the following
claims.
* * * * *